The director of the F.B.I., Robert S. Mueller III, acknowledged today for the first time that the attacks of Sept. 11 might have been preventable if officials in his agency had responded differently to all the pieces of information that were available.

As a result, Mr. Mueller said he was beginning an overhaul of the Federal Bureau of Investigation to aim more resources toward what he asserted is now its fundamental mission : the prevention of new terrorist operations. The changes, he said, are designed to bolster the bureau's capability to analyze information about terrorist threats and anticipate possible attacks.

"I cannot say for sure that there wasn't a possibility we could have come across some lead that would have led us to the hijackers," Mr. Mueller told reporters after listing several missed opportunities by officials to discern a pattern of terrorist planning before Sept. 11.

He also said that while there was no specific warning, "that doesn't mean that there weren't red flags out there, that there weren't dots that should have been connected to the extent possible."

He said that the changes he was putting into place, including reassigning hundreds of agents from the war on drugs to the war on terrorism, were designed to produce "a redesigned and refocused F.B.I."

At the heart of the changes, he said, is an effort to strengthen the bureau's analytic capability by creating an Office of Intelligence to coordinate information. More than 400 new analysts would be added to the bureau, both in the field offices and the Washington headquarters, including 25 officers on loan from the Central Intelligence Agency.

"In essence, we need a different approach that puts prevention above all else," he said. "We have to develop the ability to look around the corner."

Mr. Mueller's statements about how the F.B.I. dealt with intelligence reports before Sept. 11 were a sharp turnabout from both the substance and tone of remarks he and other other administration officials made in the weeks after the attacks on the World Trade Center and the Pentagon. As recently as May 8, Mr. Mueller told a Senate hearing that there was nothing the agency could have done to prevent the attacks.

But that stance became increasingly untenable in recent weeks after news reports that two F.B.I. field offices might have had important pieces of information that were never connected by officials at headquarters. Agent Kenneth Williams of the Phoenix office sent a memo on July 10 warning that Osama bin Laden might be sending operatives to American aviation schools to prepare for terrorist operations.

The second piece of intelligence involved Zacarias Moussaoui, a 33-year-old flight student who was arrested in Minneapolis in August
on immigration charges after F.B.I. agents were told by a manager at the Pan Am International Flight Academy that he had been acting suspiciously. Agents in the field office wanted headquarters to press for a warrant to allow them to search the computer owned by Mr. Moussaoui, who officials now believe was meant to be the 20th hijacker.

A letter sent to Mr. Mueller on May 21 by Coleen Rowley, a veteran agent and general counsel
in the Minneapolis office, seemed to put an end to the bureau's posture that no information was available that could have led to thwarting the terrorist plot.

Ms. Rowley, in an anguished 15-page letter, complained that officials in Washington blocked the field office's request to investigate Mr. Moussaoui further. She charged that an F.B.I. supervisor had played down information obtained from French intelligence authorities that would have helped obtain the needed authorization for the warrant from a special national security court.

More darkly, she said that officials at the bureau were "circling the wagons" and she warned Mr. Mueller he should stop saying no information
existed that could have prevented the Sept. 11 tragedies.

Today, Mr. Mueller lauded Ms. Rowley. "Let me take a moment to thank Ms. Rowley for her letter," he said. "It is critically important that I hear criticisms of the organization, including criticisms of me, in order to improve the organization."

Mr. Mueller said the Minneapolis and Phoenix situations should have been handled differently.

The memorandum from Agent Williams, Mr.
Mueller said, should have been shared with the C.I.A. In addition, "We should have had mechanisms in place so that something like that goes up to the top, goes up through the organization so that it is evaluated."

Most important, he said the bureau "should have analytical capabilities to put that piece together, with say, Moussaoui." He said that the Moussaoui information and the Phoenix memo went to the same unit at headquarters but no connection was made.

Regarding Mr. Moussaoui, Mr. Mueller complimented the agents in Minneapolis for their work and said that officials at headquarters should have been more supportive of their efforts to obtain search warrants from the special security court.

Mr. Mueller said he had referred the actions of the supervisors to the Justice Department's inspector general.

He disclosed there was another piece of information that
was never analyzed in conjunction with the Minneapolis or Phoenix memorandums. In 1998, a bureau pilot taking off from a commercial field in Oklahoma City recorded his suspicions
about the behavior of a group of flight students from Middle Eastern nations he encountered there. Mr. Moussaoui had taken flight lessons in nearby Norman, Okla., before he traveled to Minnesota last August. F.B.I. agents learned of that shortly after arresting him on Aug. 15.

In the future, Mr. Mueller said, people will be looking at such memorandums and determining whether they "should be put in a larger matrix from which the intentions of terrorists can be discerned."

He added, "It is critically important that we have that connection of dots that will enable us to prevent the next attack."

After Sept. 11, Attorney General John Ashcroft said repeatedly that he would shift the mission of the Justice Department to preventing another terrorist attack. Mr. Mueller's reorganization plan, some of which has to be approved by Congress, is the first tangible result of that approach.

As he sets about reassigning 400 of the bureau's 11,500 field agents from narcotics investigations to counterterrorism, Mr. Mueller said he was confident that the Drug Enforcement Administration would be able to pick up the slack. The move would reduce agents assigned to narcotics from 2,500 to 2,100, he said.

He said the bureau needed to shift to its new priorities of protecting the United States from terrorist attacks and grapple better with foreign intelligence operations.

Another 59 agents would be reassigned to counterterrorism from white-collar crime investigations and an additional 59 from the violent crimes unit.

"Looking at it right now, I can't say for sure it would not have, that there wasn't a possibility that we could have come across some lead that would have led us to the hijackers."FBI Director Robert Mueller

FBI Director Robert Mueller, acknowledging serious lapses in how the FBI mishandled some information prior to Sept. 11, suggested for the first time that investigators might have detected the terrorist plot if they had pursued leads more diligently.

Mueller's acknowledgment came amid two new disclosures of what could be missed hints about Sept. 11.

The first was a warning from another agency to the FBI that a Middle Eastern country was seeking to buy commercial flight simulators. The second was a memo from an Oklahoma City FBI agent who reported observing large numbers of Middle Eastern pilots and flight students in his area. Neither memo apparently drew much attention at the time.

"The jury is still out on
all of it," Mueller said Wednesday at FBI headquarters. "Looking at it right now, I can't say for sure it would not have, that there wasn't a possibility that we could have come across some lead that would have led us to the hijackers."

On Thursday, Mueller told ABC's "Good Morning America" :

"I do not believe, based on what I know now, that we
could have prevented the attack. I'm not ruling out the possibility at all. We could have
gotten lucky. Absolutely. But from what I've seen now, I do not believe we could have prevented the attack."

Mueller's remarks came after his announcement of a broad reorganization of the FBI, partly because of its failure to predict the attacks.

The FBIís Web site listed the following, in order, as the bureauís new list of priorities :

Protect the United States from terrorist attack

Protect the United States against foreign intelligence operations and espionage

Protect the United States against cyber-based attacks and high-technology crimes

Combat public corruption at all levels

Protect civil rights

Combat transnational and national criminal organizations
and enterprises

Combat major white-collar crime

Combat significant violent crime

Support federal, state, local and international partners

Upgrade technology to successfully perform the FBIís mission.

President Bush endorsed the sweeping changes at the FBI on Thursday, saying the bureau "didn't meet the times" in the run-up to the Sept. 11 terrorist attacks.

"The FBI needed to change," he said. "It was an organization full of
fine people who loved America but the organization didn't meet the times."

Mr. Bush's support came as Attorney General John Ashcroft announces loosened restrictions on domestic
spying, handing the FBI authority to monitor Internet sites and libraries.

"We intend to honor our Constitution and respect the freedoms that we hold so dear" and "we want to make sure we do everything we can to prevent a further attack, to protect America," Mr. Bush said.

The American Civil Liberties Union has criticized the loosening of restrictions on domestic spying, saying they could renew abuses of the past.

The new terrorism guidelines give FBI agents more freedom to investigate terrorism even when they are not pursuing a particular case.

Under existing rules, FBI agents are not allowed to do general research on the Internet or at public libraries unless the information sought directly relates to a current investigation or to leads being checked out.

The new rules also will make it easier for FBI agents to begin and pursue terrorism investigations without approval from FBI headquarters; give local FBI officials more authority to approve undercover operations in emergency situations; and let agents conduct preliminary investigations for up to six months without special approval from headquarters.

Mueller,
who took over as FBI director just days before Sept. 11, is the first senior official in the Bush administration to say that counterterrorism investigators might have detected and averted the attacks if they had recognized what they were collecting. That question is the focus of a congressional inquiry, and almost certain to come up next week during Senate Judiciary Committee hearings on the FBI's reorganization plans.

Mr. Bush has bristled over suggestions that the government had collected enough clues to stop the attacks. "Had I known that the enemy was going to use airplanes to kill on that fateful morning, I would have done everything in my power to protect the American people," Mr. Bush said earlier this month.

The FBI disclosed two other clues Wednesday that it said might be relevant to the investigation into the September hijackings. A Middle Eastern country where U.S. shipments are restricted sought unsuccessfully before Sept. 11 to buy a commercial flight simulator, and an FBI pilot in 1998 expressed concerns to a supervisor
in Oklahoma City about a number of Arab men seeking flight training.

The unidentified pilot told his supervisor "that he has observed large numbers of Middle Eastern males receiving flight training at Oklahoma airports in recent months," according to a copy of the one-page memo, under the heading "Weapons of Mass Destruction." The FBI memo, dated May 18, 1998, was marked "routine" and never was forwarded to headquarters.

The pilot added that "this is a recent phenomenon and may be related to planned terrorist activity."
He also "speculates that light planes would be an ideal means of spreading chemical or biological agents."

The FBI would not identify the country that sought to buy the simulator except to say it was not one publicly connected to Sept. 11. It said the information was given to the FBI by another U.S. agency that it would not identify.

"We need to change and indeed are changing," FBI Director Robert Mueller said at a press conference Wednesday.

Backing away from previous strong assertions that the September 11 attacks could not have been thwarted, FBI Director Robert Mueller now doesn't rule out that "tidbits of information" could have led authorities to the hijackers.

Mueller made the acknowledgment during a question-and-answer session Wednesday with reporters, following a news conference at which he outlined a massive overhaul of the nation's top law enforcement agency to focus on preventing terrorism.

"Putting all the pieces together over a period of time, who is to say?" he said.

Pressed further, the director said, "I can't say for sure that there wasn't a possibility that we would have come across some leads that would have led us to the hijackers."

Mueller insisted there was no single piece of information before September 11 that could have prevented the attacks.

Thursday, speaking on ABC's "Good Morning America", Mueller said he still doesn't believe the attacks could have been prevented. But his comments were not absolute.

"As I said before, it's not totally impossible that perhaps we would have gotten lucky, but the main point is we have to do better job in the future," Mueller said "I don't think we blew anything," Mueller added, but he acknowledged, "There were signals out there we should have picked up on."

There were "little tidbits of information that related to either flight schools, or the like, that come from some years back."

In the immediate days following the attacks, top government officials said there were no hints of what was to come on September 11. Later, the FBI amended its public comments to say that even if there were some disparate clues, there was no way the attacks could have been prevented.

But that stance was undermined by a devastating memo from an FBI whistleblower who says the agency's headquarters stymied
efforts by the Minneapolis field office to learn more about suspected terrorist Zacarias Moussaoui. Moussaoui was arrested on an immigration charge about three weeks before the deadly hijackings and had aroused suspicion at a Minnesota flight school.

FBI headquarters rebuffed the Minneapolis agents' request for a warrant to search Moussaoui's computer and investigate him further. Moussaoui has since been charged as a conspirator in the September 11 attacks.

The FBI agent who wrote the memo to Mueller, Coleen Rowley,
challenged Mueller's earlier comments that nothing could have undermined the plot.

"The
truth is, as with most predictions into the future, no one will ever know what impact, if any, the FBI's following up on those requests, would have had," Rowley wrote. (Read the memo on Time.com)

Her letter followed disclosures that an FBI agent in Phoenix had written a memo last July, one in which he questioned whether Osama bin Laden was involved in a plot involving a large number of Arab men taking aviation lessons in the United States.

On Wednesday, the FBI revealed other potential warnings that apparently did not set off any alarm bells at FBI headquarters.

In one case, the FBI's chief pilot in Oklahoma City observed that Middle Eastern men were taking flight training in the state, which the pilot speculated "may be related to planned terrorist activity," according to an FBI memo dated May 18, 1998 -- more than three years before the attacks.

The agent described the training as "a recent phenomenon." He also speculated "that light planes would be an ideal means of spreading chemical or biological agents," the memo said.

The memo was titled "Weapons of Mass Destruction," but its importance was labeled "routine."

In addition to that memo, another federal agency had been provided a document that said
operatives for another government had unsuccessfully attempted to purchase a flight simulator in the United States.

The nation involved was identified only as a Middle Eastern country. Another FBI official said it was a "restricted country."

Although the attempted purchase appeared to have no obvious connection to terrorism, the official said the FBI is attempting to get the necessary clearances to release documents related to the simulator, as well as information related to the Oklahoma City memo.

"Right now, if it has anything to do with aviation, we want to release it," the official said.